We will do whatever it takes to restore public confidence in the food they buy and eat.

Bosses at Tesco, Asda, Sainsbury’s and Morrisons

The Prime Minister said the industry had not done enough to reassure consumers.

Bosses at Tesco, Asda, Sainsbury’s and Morrisons were among 11 big retailers who signed the letter denying claims of a wall of silence.

It said they shared shoppers’ “anger and outrage”.

It added: “We will do whatever it takes to restore public confidence in the food they buy and eat.”

Tesco chief executive Philip Clark issued his own video apology to customers on the chain’s website.

He said: “We pledge that over the weeks and months ahead, we will open up our supply-chain and give you more information than any retailer has before to enable you to make informed choices about the food you buy for your family.”

Downing Street sources welcomed the letter, saying: “Consumer confidence is one of the things that has been missing and that needs the retailers to explain themselves, and what they have been doing.”